Field of the Invention
The present invention relates to a method of driving a display apparatus, and more particularly, to a display apparatus for performing external compensation through a sensing line.
Discussion of the Related Art
A flat panel display (FPD) apparatus is applied to various electronic devices such as portable phones, tablet personal computers (PCs), notebook computers, monitors, etc. Examples of the FPD apparatus include liquid crystal display (LCD) apparatuses, plasma display panel (PDP) apparatuses, organic light emitting display apparatuses, etc. Recently, electrophoretic display (EPD) apparatuses are being widely used as one type of the FPD device.
In the display apparatuses, the organic light emitting display apparatuses use a self-emitting apparatus and thus have a fast response time, high emission efficiency, high luminance, and a wide viewing angle.
The organic light emitting display apparatuses are self-emitting apparatuses where an organic light emitting diode (OLED) emits light through a recombination of an electron and a hole to display an image, and have a fast response time and low consumption power. Since the organic light emitting display apparatuses use a self-emitting device, the organic light emitting display apparatuses have an excellent viewing angle. Therefore, the organic light emitting display apparatuses are attracting much attention as next-generation FPD apparatuses.
However, in a related art organic light emitting display apparatus, a deviation of characteristics such as a threshold voltage (Vth) and a mobility of a driving transistor occurs in each of a plurality of pixels due to causes such as a process differential, deterioration, and/or the like. Therefore, the amounts of currents for driving a plurality of OLEDs differ, and for this reason, a luminance deviation between pixels occurs.
To solve such a problem, an external compensation method that corrects input image data to compensate for a characteristic change of a driving transistor included in each pixel is disclosed in Korean Patent Publication No. 10-2013-0066449 (hereinafter referred to as a prior art reference).
FIG. 1 is an exemplary diagram for describing a method of performing sensing for external compensation in a related art organic light emitting display apparatus.
A plurality of pixels should be continuously sensed for performing external compensation.
For example, when red pixels, white pixels, green pixels, and blue pixels are provided on one horizontal line n, the related art organic light emitting display apparatus first senses and stores threshold voltages or mobility of the red pixels as illustrated in portion (a) of FIG. 1, subsequently senses and stores threshold voltages or mobility of the white pixels as illustrated in portion (b) of FIG. 1, subsequently senses and stores threshold voltages or mobility of the green pixels as illustrated in portion (c) of FIG. 1, and finally senses and stores threshold voltages or mobility of the blue pixels as illustrated in portion (d) of FIG. 1. Subsequently, related art organic light emitting display apparatus repeats the above-described operation on a plurality of pixels which are provided on a next horizontal line.
However, as a size of a panel is enlarged and the image quality of the panel is far more sharpened, a period which is required for sensing characteristics (threshold voltages or mobility) of the pixels is progressively increasing.
For example, 2,160 horizontal lines are provided in a panel applied to an ultra-high definition (UHD) display apparatus, and when the panel is configured with red (R), green (G), blue (B), and white (W) pixels, 15,360 (=3840×4) pixels are provided on one horizontal line.
In this case, sensing is performed 8,640 (=2160 lines×4) times for sensing all pixels provided in a whole panel by using a method illustrated in FIG. 1.
Therefore, in the panel, a long period is required for sensing all the pixels.
Generally, the sensing operation is performed during a blank time between frames or when a display apparatus is turned off. Therefore, when the sensing period becomes longer, it is difficult to sense all pixels during the blank time. Also, even when the display apparatus is turned off, it is difficult to normally sense all the pixels. When the blank time becomes longer, a period where an image is displayed becomes shorter, causing the degradation in image quality. For this reason, it is difficult to increase the blank time depending on the sensing period.
FIG. 2 is an exemplary diagram for describing a method of calculating a sensing value of a pixel, where sensing is not performed, by using an mean value in an organic light emitting display apparatus.
As described above, as a size of a panel is enlarged and the image quality of the panel is far more sharpened, a sensing period for sensing characteristics of all pixels increases. For this reason, it is difficult to sense the characteristics of all the pixels during a limited period.
To solve such a problem, a method of calculating a sensing value illustrated in FIG. 2 has been proposed.
For example, as illustrated in FIG. 2, sensing is substantially performed for four pixels, and sensing values are collected. Sensing is not performed for one pixel (hereinafter simply referred to as a non-sensing pixel) surrounded by the four pixels (hereinafter simply referred to as sensing pixels). In this case, a sensing value of the non-sensing pixel is calculated based on an mean value of the sensing pixels.
However, as illustrated in FIG. 2, when at least one of the sensing pixels is a defective pixel, the sensing value of the non-sensing pixel is large in error.
For example, in a case where a sensing value of 500±100 is a sensing value of a normal pixel and a sensing value of a defective pixel which is not normally driven is 0, although the non-sensing pixel in the middle of the sensing pixels is a normal pixel, when a related art method of calculating a sensing value by using an mean value is applied, a sensing value of the non-sensing pixel is calculated as 383.
Therefore, although an actual compensation value is within a range of 500±100, the non-sensing pixel is compensated for by an abnormal external compensation value, and for this reason, the non-sensing pixel is abnormally driven.